Deep drawing cold rolled rimmed steel sheet and strip and production of the same



March 8, 1966 HIROSH; YOSHIDA 3,239,389

1 DEEP DRAWING coLD ROLLED RIMMED STEEL SHEET AND STRIP AND PRODUCTION OF THE SAME Filed June 11, 1963 United States Patent C) Japan Filed June 11, 1963, Ser. No. 286,995 Claims priority, application Japan, Oct. 18, 1962, 37/ 46,275 12 Claims. (Cl. 148-2) The present invention relates to the cold rolled. rimmed steel sheet and strip having a preferred orientation adapted for ress rdrmin'g'andthe"preductien 'o'fthe same.

Heretotor'e an aluminum stabilized steel has been widely employed as a deep drawing steel sheet and strip. The aluminum stabilized steel sheet or strip is produced by the steps "of making a steel ingot which has been deoxidized to 'a high degree by aluminum in an ingot casting 'step followed by a hot rolling step and a cold rolling one, and annealing the steel sheet or strip to precipitate aluminum nitride, whereby an elongated "grain structure is formed in it. "In reference'to the reason why the aluminum stabilized steel sheet or strip has a superior deep drawing property, it has heretofore been attributed to the fact that the elongated grain structure has caused the deformation resistance in a thickness direction to be greater than the deformation resistance in a plane so that the thinning in thickness has 'be'enreduced.

However, after an extensive study of the aluminum stabilized steel sheet or strip 'by means of the X-raydiffraction method, it has been found that the excellent deep drawing property of the aluminum stabilized steel sheet or strip is not attributed to the form of grains, but to the preferred orientation caused by the conditions of the steel sheet or strip making process.

Having our attention focused/on the conditions of the steel sheet or strip production advantageous for the formation of the preferred orientation favorable to the deep drawing quality together with the eifect of addition of minor elements, I, inventor, have completed the present invention.

The steel sheet or strip provided with the above quality in accordance with this invention has been accomplished by the process comprising the steps of adding lead or lead and one or more of the-elements selected from the group consisting of antimony, bismuth and niobium into a molten steel produced by the open hearth furnace, the electric furnace or the converter in either a steel making or ingot casting step to obtain rimmed steel ingots containing lead. or lead and one or more of said elements singly or combined in a'total amount of 0.0030.100% by weight, then subjecting said steel to hot and. cold rolling, then annealing the cold rolled rimmed steel sheet or strip at a temperature of 500-7 50 C. in an atmosphere containing hydrogen and moisture to decarburize its carbon content less than 0.020% or decarburize and denitride its carbon content less than0.020% and its nitrogen con tent less than 0.002%.

The decarburizing annealing step and. the decarburizing and denitriding annealing one described in the present invention are achieved by subjecting the cold rolled rimmed steel sheet or strip to an anneal in an atmosphere Patented Mar. 8, 1966 ICC containing hydrogen and moisture at the temperature of 500-750 C. for a predetermined period of time. The period of time required for the anneal depends upon the steel sheet thickness and the composition of the atmosphere. In reference to the behavior of carbon and nitrogen in the annealing process, the velocity of decarburization is relatively so fast that carbon is removed sufficiently at an early period of the anneal, but, on the other hand, the velocity of denitridation is so low even in an atmosphere, such as, AX gas, containing a low nitrogen content that it will take a pretty long period of time until a desired low nitrogen content is attained in the steel sheet. However, denitridation is hardly effected even in the atmosphere containing a high nitrogen to decrease the carbon and nitrogen contents thereof as low as possible by subjecting it to annealing in the atmosphere consisting of a major part of H and a minor part of N and H 0.

From an economical point of view for the purpose of attaining a low cost production of a steel sheet having a good drawability with an inferior non-aging property, an annealing step in the atmosphere consisting of a major part of N and a minor part of H and H 0, such as DX gas with appropriate moisture, for a relatively short period with a view to decarburizing only is relied upon to produce a cold rolled rimmed steel sheet or strip having a better drawability than that of the commercial one of prior art.

A preferred embodiment of this invention comprises making steel by the known basic open hearth furnace, adding lead to the thus obtained molten steel, and producinga rimmed steel ingot containing 0.060% carbon and 0.035% lead.

Then, a cold rolled strip coil of 0.8 mm. in thickness is produced by the known process of slabbing, hot rolling and cold rolling.

Subsequently, this strip coil is subjected to a decarburizing annealing in an open coil annealing furnace at about 700 C. for a period of 40 hours in DX atmosphere with moisture, and to known skin pass rolling, which results in the production of excellent deep drawing cold rolled. steel sheet and having the following prop- 'erties: E 1.55, Er 11.70 mm., C.C.V. 36.65 mm, T.S.

the present steel sheet are listed as No. 14 data in Table 1.

Another preferred embodiment of this invention comprises making steel by the known basic open hearth furnace, adding lead to the thus obtained molten steel, and producing a rimmed steel ingot containing 0.08% carbon and 0.030% lead. Then, a cold rolled strip coil of 0.8 mm. in thickness is produced by the known process of slabbing, hot rolling and cold. rolling. Subsequently, this strip coil is subjected to a decarburizing and denitriding annealing in an open coil annealing furnace at about 700 C. for a period of 40 hours in AX atmosphere with moisture, and to known skin pass rolling, which results in the production of excellent deep drawing cold rolled steel sheet and having the following properties: 1.55, Er 11.8, C.C.V. 36.6, T.S. 29.4 kg./mm. and El. 48%.

tion

inven rimmedsteel, 7 the alum Chemical Analysis le figure method, all of which have been TABL l Chemical Analysis The excellent propertiestsof the steel: sheet or st Steel Mechanical Properties EL, percent any other steel sheet or strip'in'thed eep drawing property.

of this invention will now be described hereinbelow in the:

following description; 7 a a Table 1 shows the plastic strain ratio (R), the conical,

cup value (C.C.V;), various mechanicaltproperties and the intensity of (111) plane diffractionpieak bythe:-

X-ray lnversepo determined on the commercial containing various amounts of lead, antimony, bismuth and niobium.

Corn. rim. steel-...

10 num stabilized steel, and the steel sheetof this inor the

s expensive tlrnony,

vide the formation of the preferred orientation favorable to the deep drawing process by the steps of adding a;m

Specimen Specimen No.

The chemical analysis and mechanical properties of the present steel sheet are listed as No. 6 data in Table .1.,,

One of the features of this invention is to pro amount of lead or lead and one or more of an bismuth and niobium to the steel and subject thus produced steel to heat treatment. The steel sheet or strip of this invention can be produced from a relatively low cost rimmed steel, therefore it is les than the aluminum stabilized steel or strip. Moreover, the steel sheet or strip of this invention is superior to LLLLLLLLLLLLLL Specimen N o.

Elongation (test specimen: JIS No. 5., gauge length=50 111111;). Er- Plflrichsen. Y.'E.=Yield Point: .El'ongationi T.S.='Te'nsile. Strength Y.P.=Yield om V 1 Drawn through.

NOTE.-El.=

TABLE 2 Chemical Analysis (Percent) Steel Si M11 P S Al Pb Nz Com. rim. steel Tr. 0.35 0.010 0. 014 Tr. Tr. 0.0022 Al stabilized steel..- Tr. 0.30 0.008 0.010 0.055 Tr. 0.0058 De-C. de-N. rim. st 'Ir. 0. 34 0.012 0.014 Tr. Tr. 0.0008 'Pb-contJdeC. de-N. rim. steel. Tr. 0. 33 0.009 0.012 Tr. 0.030 0.0008

Punch Shape Round Round T Round Round Flat Flat Blank dia., mm.

Steel Blank Holder Pressure (ton) Measurement Stretch Stretch Stretch Flange Flange Flange Depth, Depth, Depth, Strain Strain Strain mm. mm. mm. ratio, ratio, ratio,

a percent a percent 04 percent Com. rim. steel 44.5 50.0 61. 5 4. 78 3. 93 9.45 Al stabilized steel 45. 0 50. 5 66. 0 7. 78 5. 94 18. 89 De-O. de-N. rim. steel 46. 5 51.0 65. 5 '7. 50 5.62 '14. 52 Pb-cont. dc-C. de-N. rim. steel 47.0 51. 5 68.0 8.95 5. 85 16. 82

NOTE.100-t011 press test. Die and Punch in detail.

.Punch shape:

(a) Round: Hemisphere. (13) Flat: Profile radius R. Punch diameter 100 min. (b Die diameter... 102.4 mm. Die profile radius 5 R. Blank holder diameter 300 nun. 1

The Japanese Industrial Standard, Z-2249, relating to 40 More particularly, the conical cup value (C.C.V.) is

the method of conical cup test, has been recently published. .In this conical cup test, it 'is possible to draw a steel'sheet without forming Wrinkles and without applying any blankholder pressure provided the correct blank diameter is selected with respect only to sheet thickness. The eflect of bending and unbending, which is an important :factor in a cylindrical cup-forming test, is also less important in'the conical cup test. A hemispherically ended punch with a profile radius of approximately 5 to 10 times the thickness of the test blank is used. The rating of-drawability is obtained from the average diameter of the rim of the conical cup when fracture occurs. Since the blank diameter is fixed .only by the sheet thickness, the test is simple and quick.

The principle of the test is illustrated in FIG. 1. I A circular blank is rested .horizontally in the conical die, and drawn with the ppropriate punch until the bottom of the cup fractures. The dimensional specifications are given in Table 3.

The die hole diameters specified are such that'no'ironing of the cup occurs as it enters the die hole. Blanks should 'be cleaned and then lubricated and the speed of drawing is virtually immaterial.

The conical cup-forming test of the Japanese Industrial Standard, Z-2249, is performed in an arrangement of tools for a conical cup :test shown in the accompanying drawing, in which:

represented by the numerical value, mm., of the average diameter of the rim of the conical cup when'fracture 'ocours as shown in FIGS. 23. The conical cup value shown in FIG. 3, which is'less than that of FIG. 2, is obtained from the steel sheet having a better deep drawability than that of the one shown in FIG. 2. The shape of the completely drawn cup with no fracture shown-in FIG. 4 is attained by the steel sheet of a very high deep drawability, and in this case, no value of conical cup test is obtained, but represented as, drawn throng in Table 1.

In order to obtain the conical cup value or C.C.V. of a steel sheet of a particular thickness, the particular tools specified by JIS Z-2249 as shown in Table 3 should be employed. C.C.V. of various steel sheet listed in Table 1 are the measurements conducted on the sheet of the thickness, 0.8 mm. by means of the die type 17 of Table 3. In Table 4, the minimum standard value for showing the drawability of each sheet of a particular thickness produced by the'process of'this invention is listed.

TABLE 4 C.O.V. oi the Sheet Thickness Die Type, sheet of this J IS invention 13 26.40 or less. 13 26.40 or less. 17 37.30 or less. 17 37.42 or less. 21 44.82 or less. 21 45.12 or less.

The plastic strain ratio, R, is a value showing the deep. drawing property and the preferred orientation suitable for the deep drawability of the steel sheet, and can be obtained from the following formula:

log t /t Where:

W =width of tensile test specimen before tension W=width of tensile test specimen after tension t =thickness of tensile test specimen before tension t=thickness of tensile test specimen after tension gauge length of the tensile test specimen by means of the electronic strain meter and the mean width of the speci- I men. The R value obtained from the following formula, provided that the volume of the deformed test specimen being constant: I 'W t Z'W't where:

l =gauge length before tension. l=gauge length after tension.

: log W /W log l-w/l -w By the above measurement,.the test errors are very small. For this test specimen ,a tensile test specimen (gauge length 50 mm.) of I IS (Japanese Industrial Standard) No. 5 is employed, and the R value in 15% extension is obtained. In generahas the R- value depends on the direction from which the test specimen is taken, .the

measurement along the three directions, rolling direction (R degrees to the rolling direction (R and degrees to the rolling direction (R is made, and the mean value Ii is obtained from the following formula: (R1 (Re +2024.)

As clearly shown in the Iivalue and the X'-ray intensity of (111) plane diffraction peak of Table 1, the crystallographic orientation of the rimmed steel sheet of. this invention containing a small amount of lead,.antimony, bismuth and niobium is different from that of the known rimmed steel sheet which has been decarburized and denitrided. Thus, the X-ray intensity of (111) plane diffraction peak of the known rimmed steel is small while that ofthe steel sheet produced from the known rimmed steel which has been subjected to the decarburizing and denitriding annealingis also relatively small.- Compared to the above, the accumulation of the main crystallographic orientatioin (111 of the present decarburized and denitrideclrimmed steel sheet containing lead,.antimony,

' bismuth and niobium is stronger.

8f 5 The intensity of (111) plane diffraction peakiofthe aluminum stabilized steel is stronger than that of the;

known rimmed steel, butweakerrthan that of'the, present steel sheet. 7 more distinct in the valueof Table 1. Thus, the i value of the commercial rimmedsteel is the leastof all, that. of i the decarburized and denitrided rimmed steel larger, and" that of the aluminumstabilized steel the largest. The E3 value of the present decarburized and denitrided rimmed 1 steelsheetcontaining lead, antimony, bismuth and 'niobium is also equal to orlarger than that-of the aluminum,

stabilized steel.

7 In case (111) plane is parallel-with the rolling surface,: the fact that v.the R value is made large can be explained theoretically as follows: when the slip direction is only [111] direction while deformation, and when (111) plane is parallel with the-rolling surface, it is explained by mathematical analysis that the. strain-in the sheet plane direction becomes larger than that in the: thickness di.-,

rection.

In Table 1, the conicalcup value of the rimmed steel sheet containing an appropriate. amount, of lead, antimony, bismuth and niobiumis good, and particularly;

the test. specimens of the sheet steel: containing 0.022% Sb+0.025,% Pb and.0. ()28% Sb+0.041% Pbare drawn through without. fracture, respectively.

As'described hereinabove, a favorable effect of lead.

and antimony, bismuth or niobium onthe deep drawing quality of the steel sheet is; apparent. .Ho'wever, in=the practical press'forming process, the formation of, miscellaneous complicated shapes is 'requiredso much thatnot only the high degree'deep .drawability butalso thez'highi stretch .formability should be given to the steel. sheet.-

reference to the characteristic value for showing stretch formability, both elongation, El, and the Erichsen value,

Er are universally adopted.

As clearly illustrated in.Tablef 1,.ther steelsheet'con taining. a suitable amount of lead'and antimony, bismuth or niobium has a good-conical cup value as well as good El and Er values.

Table '2. shows the results ,of'various: practical'press forming tests conducted on various steel-sheet. In each press forming test'shown in Table 2, the stretch form-,

ability refers to the left side/while the deep drawability to the right more emphatically than the other, respectively.

In the press forming requirements,.the greater the blank holder'pressure, the larger the blank,diameter, and the round punch ratherthan the flat one will all 'favorthe stretch formability more ,emphaticallyinthe press'form ing test. Three-measurements in the left refer to the depth, mm., of penetration when fracture occurs. Three values in the right refer tothe flange strain ratio at: 5 I

. 0 I i where:

D =blank diameter, before press "forming D =mean diameter after. press forming As is'evident from Table 2,. the deep drawing property of the commercial-rimmed steel sheet is considerably in.-

ferior to thatof other steel. sheet-for the same purpose, but the stretch formability thereof is relatively goodl The aluminum stabilized steel. sheet shows the, mean values both in the deep drawability and stretch'formability.

' Compared to the above the decarburized and denitridedv rimmed steel sheetior strip containing lead and antimony, bismuth or niobiumof the present invention hasznot only the excellent deep'drawing property but; also the good stretch ,formability. It will be appreciated, therefore,, that this steel sheet or strip is well suited for all'typ e of i press forming. V

As to the agingpropertyofrthe present steel sheet, the

aging velocity thereof is considerably slower. than that of.

the commercial rimmed steel sheet of prior art, and if the The above-mentioned relationship is made carbon and nitrogen content can be reduced by the decarburizing and denitriding annealing, the present steel will be given the non-aging property. However, from an industrial and economical point of view, it will be adequate if no stretcher-strains occur in press forming. The steel sheet or strip of the invention will have an adequate non-aging quality if the elements, carbon, nitrogen, lead, antimony, bismuth and niobium are contained in the steel in the above-mentioned range.

I claim:

1. A method for producing cold rolled rimmed steel sheet and strip having good drawability and stretchability comprising the steps of adding lead to molten steel to produce a rimmed steel containing said element in an amount of 0.0030.100% by weight, making a cold rolled rimmed steel sheet or strip through hot and cold rolling procedure, and subjecting said steel sheet or strip to a decarburizing anneal to decrease its carbon content to less than 0.020% by weight.

2. A method for producing cold rolled rimmed steel sheet and strip having good drawability and stretchability represented by a conical cup value determined by the conical cup test specified by the Japanese Industrial Standard Z-2249, said value being less than 37.30 for a sheet of the thickness of 0.8 mm. and dependent on a thickness selected from the range of 0.5 to 1.6 mm., comprising the steps of adding lead to molten steel to produce a rimmed steel containing said element in an amount of 0.003- 0.100% by Weight, making a cold rolled rimmed steel sheet or strip through hot and cold rolling procedure, and subjecting said steel sheet or strip to a decarburizing anneal to decrease its carbon content to less than 0.020% by weight,

3. The method as claimed in claim 1, in which at least one element selected from the group consisting of antimony, bismuth and niobium is added with the lead.

4. The method as claimed in claim 2, in which at least one element selected from the group consisting of antimony, bismuth and niobium is added with the lea-d.

5. A method for producing cold rolled rimmed steel sheet and strip having good drawability and stretchability comprising the steps of adding lead to molten steel to produce a rimmed steel containing said element in an amount of 0.0030.100% by weight, making a cold rolled rimmed steel sheet or strip through hot and cold rolling procedure, and subjecting said steel sheet or strip to a decarburizing and denitriding anneal to decrease its carbon content to less than 0.020% and its nitrogen content to less than 0.002%.

6. A method for producing cold rolled rimmed steel sheet and strip having good drawability and stretchability represented by a conical cup value determined by the conical cup test specified by the Japanese Industrial Standard Z-2249, said value being less than 37.30 for a sheet of the thickness of 0.8 mm. and dependent on a thickness selected from the range of 0.5 to 1.6 mm., comprising the steps of adding lead to molten steel to produce a rimmed steel containing said element in an amount of 0.003 0.100% by weight, making a cold rolled rimmed steel sheet or strip through hot and cold rolling procedure, and subjecting said steel sheet or strip to a decarburizing and denitriding anneal to decrease its carbon content to less than 0.020% and its nitrogen content to less than 0.002%.

7. The method as claimed in claim 5, in which at least one element selected from the group consisting of antimony, bismuth and niobium is added with the lead.

8. The method as claimed in claim 6, in which at least one element selected from the group consisting of antimony, bismuth and niobium is added with the lead.

9. A cold rolled, decarburized rimmed steel sheet and strip characterized by good drawability and stretchability, said steel consisting essentially of 0.0030.l00% lead, less than 020% carbon, OAS-0.60% manganese, and the balance iron and incidental impurities.

10. The steel sheet and strip according to claim 9 which includes at least one element selected from the group consisting of antimony, bismuth and niobium.

11. The steel sheet and strip according to claim 9 wherein the nitrogen content is less than 0.002%.

12. The steel sheet and strip according to claim 10 wherein the nitrogen content is less than 0.002%.

References Cited by the Examiner UNITED STATES PATENTS 2,095,580 10/1937 Whetzel 14812 2,271,242 1/ 1942 Altenburger 14816 2,360,868 10/1944 Gensamer 14816 2,378,548 6/1945 Gregg 123 2,999,749 9/ 1961 Saunders et al. 75-58 3,102,831 9/1963 Tisdale 14812 3,105,780 10/1963 Low 14816 OTHER REFERENCES Archiv fur das Eisenbuttenwesen, volume 8, 19345, pages 263-67.

DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, Examiner.

O. D. MARJAMA, Assistant Examiner. 

1. A METHOD FOR PRODUCING COLD ROLLED RIMMED STEEL SHEET AND STRIP HAVING GOOD DRAWABILITY AND STRETCHABIITY COMPRISING THE STEPS OF ADDING LEAD TO MOLTEN STEEL TO PRODUCE A RIMMED STEEL CONTAINING SAID ELEMENT IN AN AMOUNT OF 0.003-0.100% BY WEIGHT, MAKING A COLD ROLLED RIMMED STEEL SHEET OR STRIP THROUGH HOT AND COLD ROLLING PROCEDURE, AND SUBJECTING SAID STEEL SHEET OR STRIP TO A DECARBURIZING ANNEAL TO DECREASE ITS CARBON CONTENT TO LESS THAN 0.020% BY WEIGHT. 